June 1, 2012 -- Researchers say gas stoves can generate lung-irritating levels of nitrogen dioxide and other indoor air pollutants.

The good news is that there's an easy fix. A new study shows that turning on the fan and cooking on the back burners can reduce levels of air pollutants by about half. The bad news is that most vent fans don't fix the problem completely.

"What we see is that range hoods can be effective on the order of 60% or 70% if they're used right or they're designed right, and that's great. But they're not 98% effective," says Glenn C. Morrison, PhD, an environmental engineer at the Missouri University of Science & Technology in Rolla, Mo. "Is that sufficient? That's still a question that a homeowner needs to consider."

Morrison studies indoor air pollution, but he was not involved in the current research.

Testing Vent Fans Over Gas Stoves

For the study, which is published in Environmental Science & Technology, researchers measured how well seven different kinds of commonly used over-the-stove ventilation systems worked. They tested energy efficiency and how well the vents captured air pollutants like nitrogen dioxide, carbon monoxide, formaldehyde, and ultrafine soot particles that are generated by gas burners and ovens. They also measured noise levels, since many people say they don't use their vent fans because they are too loud.

Some models had hoods to temporarily trap rising gasses. Others were flat on the bottom with fans that pulled air through grease screens. Prices of the vents ranged from $40 to $650.

All the exhaust systems were designed to vent to the outdoors. Researchers say the kind of over-the-stove fans that suck air in but then blow it back out into the same room don't really do much to decrease pollution levels.

None of the systems worked well in all three areas. The one that worked the best at clearing pollutants from the air was also so loud that it made normal conversation impossible. Two that were quiet and cleared 70% to 90% of pollutants from the air had high fan speeds that made them energy hogs.

But all the exhaust systems worked better over the two back burners of a four-burner stove.

"If you're cooking on the front burners and you turn the fan on, you can remove 25% of the pollution, but if you cook on the back burners you'll remove twice as much," says researcher Brett C. Singer, PhD, a civil and environmental engineer at Lawrence Berkeley National Laboratory in Berkeley, Calif.

The reason, Singer says, is that hot air rises in a column over each burner and many ventilation systems only extend over the back half of stovetop, missing the front burners.

Gas Stoves May Be a Source of Indoor Air Pollution

How much air pollution can a gas stove generate? Singer says an upcoming study will show that the levels of nitrogen dioxide generated by a gas stove can exceed the EPA's safe limits for outdoor air.

"There are few if any places that exceed those outdoor standards for nitrogen dioxide," Singer says.

"But indoors, millions of Americans are exposed to those levels from using their gas stoves without venting. For most of those people, if they used their venting range hood, they'd be fine," he tells WebMD.

Nitrogen dioxide is a corrosive gas that can irritate the lining of the eyes, nose, throat, and respiratory tract.

According to the EPA, exposure to even low levels of nitrogen dioxide can make it more likely that people with
asthma will suffer attacks. It can also decrease lung function in people with chronic obstructive pulmonary disease (COPD) and increase the risk of respiratory infections, especially in young children.

If you have a gas stove, researchers advise doing three things to increase the health of your indoor air:

Make sure the fan over the stove vents to the outside. If it doesn't, consider having a better exhaust system installed. In general, vents that best captured pollutants use metal hoods to temporarily trap gas and soot so the fan can blow them outside.